The exponential growth in the demand of wireless data communications has put a tremendous pressure on the cellular network operators to improve the capacity of their communication networks. To improve the spectral efficiency of these networks, scarce radio resources have to be reused aggressively in neighboring cells. As a result, inter-cell interference has become a main source of signal disturbance, limiting not only the service quality of the cell-edge users, but also the overall system throughput.
Coordinated multi-point (CoMP) transmission or reception is one known means to effectively mitigate inter-cell interference. FIG. 1 depicts a representative CoMP cluster 10, in which User Equipment (UE) 12 receive wireless communication service in a number of conventional cells 14. A base station or eNode B 16 transmits downlink RF signals to UE 12 (and receives uplink transmissions from the UE 12) in each cell 14. To avoid inter-cell interference, a central processor (CP) 30 coordinates downlink transmissions to, and possibly also uplink transmissions from, UE 12 in the cells 14 forming the CoMP cluster 10. The CP 30 coordinates and optimizes transmissions to reduce or even avoid mutual interference among UE 12. The benefit attainable by the deployment of CoMP systems hinges on how well such coordination can be performed by the CP 30.
To enable the CP 30 to effectively coordinate transmission and/or reception at multiple cells 14, timely signal information must be communicated between remote base station sites 16 and the CP 30. However, the amount of information needed to send to or receive from each base station 16 can be overwhelming, especially when multiple antennas are deployed at each site. In general, the CP 30 generates, and must transmit to remote base stations 16, the In-phase (I) and Quadrature (Q) components of complex-valued downlink signals to be transmitted by each antenna at each base station 16. Additionally, each base station 16 must transmit to the CP 30 the complex-valued IQ signal received at each antenna.
In the standard Common Public Radio Interface (CPRI), each real-valued sample of the IQ backhaul signal would simply be quantized independently by a fixed number of bits (e.g., 16). CPRI transmission does not exploit any structure of the underlying backhaul signal, and is an inefficient way of representing wireless communication signals. CPRI transmission of IQ wireless signals thus places a large burden on the capacity of backhaul links, which may limit the performance otherwise achievable by CoMP systems.
Other systems may additionally perform precoding at a processing unit of a network, for transmission by base stations. All such systems require voluminous data transfer between the network processing unit and base stations.